1. Field of the Invention
The present invention relates to a semiconductor laser device which can reduce variations in the wavelength of light emitted from a semiconductor laser element.
2. Description of the Related Art
As shown in FIG. 7, a conventional semiconductor laser device 100 is provided with a semiconductor laser element 102 and a light detecting element 104. The semiconductor laser element 102 emits a light beam L1 (hereinafter called xe2x80x9cemitted light L1xe2x80x9d when appropriate) toward a photosensitive material. The light detecting element 104 detects a light beam L2 (hereinafter called xe2x80x9cdetected light L2xe2x80x9d when appropriate) which is emitted separately from the semiconductor laser element 102 in order to detect the amount of light of the emitted light L1.
At the semiconductor laser device 100, in order to suppress variations in the emitted light L1 which is emitted from the semiconductor laser element 102, so-called auto power control (APC) is utilized in which the driving circuit of the semiconductor laser element 102 is controlled such that the light amount of the detected light L2 detected at the light detecting element 104 is made constant.
Because the sensitivity of the light detecting element 104 varies due to the temperature thereof, the detected light L2 cannot be detected accurately, and accurate AP control cannot be carried out. Further, due to the variations in the temperature of the semiconductor laser element 102 itself, the wavelength of the detected light L2 emitted from the semiconductor laser element 102 varies, and accurate AP control cannot be carried out.
In order to overcome the aforementioned problems, in the conventional semiconductor laser device 100, the semiconductor laser element 102 and the light detecting element 104 are mounted to a thermally conductive material 108 which contacts a heat generating element 106, such that the respective temperatures of the semiconductor laser element 102 and the light detecting element 104 are regulated. However, the light detecting element 104 does not actually detect the output light L1 which is illuminated onto the photosensitive material, and detects the detected light L2 which is separate therefrom. Therefore, in this case as well, accurate AP control cannot be carried out.
In view of the aforementioned, an object of the present invention is to provide a semiconductor laser device which can carry out accurate AP control by directly detecting output light which is illuminated onto a photosensitive material.
A first aspect of the present invention is a semiconductor laser device comprising: an emitting device which emits a light beam which is illuminated onto a photosensitive material; a light-amount detecting device which detects an amount of light of the light beam which is illuminated onto the photosensitive material; a single or plural temperature-adjusting devices which adjust a temperature of the emitting device and a temperature of the light-amount detecting device to constant temperatures; and a control device which controls the amount of light of the light beam emitted from the emitting device, on the basis of the amount of light of the light beam detected by the light-amount detecting device.
Next, the operation of the semiconductor laser device of the first aspect of the present invention will be described.
The emitting device which emits a light beam is provided at the semiconductor laser device. The light beam emitted from the emitting device is illuminated onto a photosensitive material, and the photosensitive material is exposed. The amount of light of the light beam emitted from the emitting device is detected at the light-amount detecting device. On the basis of the amount of light of the light beam detected at the light-amount detecting device, the control device controls the amount of light of the light beam emitted from the emitting device (so-called AP control).
Here, the respective temperatures of the emitting device and the light-amount detecting device are adjusted to constant temperatures by the temperature-adjusting device. Thus, effects due to the temperature characteristics of the emitting device and the light-amount detecting device can be avoided. Namely, although the emitting ability of the emitting device and the detecting ability of the light-amount detecting device vary due to changes in temperature, the emitting ability and detecting ability can be kept constant by adjusting the temperatures of the emitting device and the light-amount detecting device to constant temperatures. Further, the wavelength of the light beam is stabilized. As a result, AP control can be carried out accurately.
In the present invention, the light beam which is illuminated onto the photosensitive material is directly detected by the light-amount detecting device. Thus, AP control can be carried out more accurately than in a case, such as that of the prior art, in which a light beam, which is other than the light beam illuminated onto the photosensitive material, is detected. Namely, in the present invention, in addition to avoiding effects due to temperature, AP control can be improved by directly detecting the light beam illuminated onto the photosensitive material.
In the semiconductor laser device of the first aspect of the present invention, preferably, the temperatures of the emitting device and the light-amount detecting device are adjusted by a single temperature-adjusting device.
In the semiconductor laser device of the first aspect of the present invention, preferably, the emitting device and the light-amount detecting device are mounted to a temperature-regulating block whose temperature is adjusted by a single temperature-adjusting device.
Next, the operation of the above-described semiconductor laser device will be described.
In the present invention, preferably, the emitting device and the light-amount detecting device are mounted to a temperature-regulating block whose temperature is adjusted by a single temperature-adjusting device. In this way, the respective temperatures of the emitting device and the light-amount detecting device can be adjusted.
Here, by providing a single temperature-adjusting device, the temperatures of the emitting device and the light-amount detecting device can be adjusted by a single temperature-adjusting device. As a result, as compared with a case in which plural temperature-adjusting devices are provided, no errors between respective temperature-adjusting devices arise, and adjustment of the temperatures of the emitting device and the light-amount detecting device is easy. Further, by using a single temperature-adjusting device, the number of parts and the number of assembly processes is reduced by that much, and fabrication of the semiconductor laser device is easy.
In the semiconductor laser device of the first aspect, more preferably, the light beam is reflected by a reflection coated optical member for beam reshaping and is detected by the light-amount detecting device.
Next, operation of the above-described semiconductor laser device will be described.
Preferably, the light beam is reflected by a reflection coated optical member for beam reshaping and is detected by the light-amount detecting device. Therefore, a reshaped light beam can be detected. Thus, because the light beam is detected in a reshaped state by the light-amount detecting device, the amount of light of the light beam can be detected accurately, and AP control can be carried out accurately.
An optical member where portion of the light beam passes and another portion of the light beam reflects may be provided in the semiconductor laser device of the first aspect of the present invention for illuminating the reflected light beam onto the photosensitive material and detecting the passed light beam through the optical member with the light-amount detecting device.
In the semiconductor laser device of the first aspect of the present invention, more preferably, a temperature-detecting device forming the temperature-adjusting device is disposed in a vicinity of the emitting device, and the temperature of the emitting device is detected by the temperature-detecting device.
Next, operation of this semiconductor laser device will be described.
Preferably, the temperature-detecting device forming the temperature-adjusting device is disposed in a vicinity of the emitting device. Thus, the temperature of the emitting device can be detected as accurately as possible. On the basis of the temperature detected by the temperature-detecting device, the temperature of the emitting device is adjusted to a constant temperature. Thus, the accuracy of adjustment of the temperature of the emitting device can be improved. As a result, the wavelength of the light beam emitted from the emitting device can be stabilized.
In the semiconductor laser device of the present invention, more preferably, a temperature-detecting device forming the temperature-adjusting device is disposed in a vicinity of the light-amount detecting device, and the temperature of the light-amount detecting device is detected by the temperature-detecting device.
Next, operation of this semiconductor laser device will be described.
Preferably, the temperature-detecting device forming the temperature-adjusting device is disposed in a vicinity of the light-amount detecting device. Thus, the temperature of the light-amount detecting device can be detected as accurately as possible. On the basis of the temperature detected by the temperature-detecting device, the temperature of the light-amount detecting device is adjusted to a constant temperature. Thus, the accuracy of adjustment of the temperature of the light-amount detecting device can be improved. As a result, the output stability of the light-amount detecting device can be improved.
More preferably, in the semiconductor laser device of the first aspect of the present invention, an angle of at least one of a reflecting surface of the optical member and a light receiving surface of the light-amount detecting device is adjusted such that the light beam is incident obliquely on the light receiving surface of the light-amount detecting device.
Next, operation of the above semiconductor laser device will be described.
In this preferable semiconductor laser device, an angle of at least one of a reflecting surface of the optical member and a light receiving surface of the light-amount detecting device is adjusted such that the light beam is incident obliquely on the light receiving surface of the light-amount detecting device. Thus, the light beam, which is reflected at the light receiving surface of the light-amount detecting device, follows the optical path of the light beam incident on the light receiving surface, and does not again reach the emitting device. As a result, a mode-hopping phenomenon, in which the light beam emitted from the emitting device is interfered with by the light beam reflected at the light receiving surface of the light-amount detecting device, can be prevented.
In the semiconductor laser device of the first aspect of the present invention, preferably, the control device includes a driving circuit substrate which is mounted to the temperature-regulating block and on which is mounted a driving element which drives the emitting device, and the driving element substantially contacts the temperature-regulating block.
Next, operation of the above-described semiconductor laser device will be described.
In this preferable semiconductor laser device, because the driving element which is mounted on the driving circuit substrate contacts the temperature-regulating block, the temperature of the driving element can be adjusted. As a result, effects of the temperature characteristic of the driving element can be avoided, and the amount of light of the light beam emitted from the emitting device can be stabilized. Further, the driving element contacts the temperature-regulating block. Thus, as compared with a case in which the driving element does not contact the temperature-regulating block and is connected by a harness, effects due to external disturbance of a harness can be avoided. Thus, the light amount of the light beam emitted from the emitting device can be stabilized.
The emitting device and the light-amount detecting device are mounted on the temperature-regulating block whose temperature is adjusted by the temperature-regulating device. The control device includes a driving circuit substrate, which has a driving element for driving the emitting device and a nonlinear circuit structural element for converting the input-output characteristics of the semiconductor laser device, is mounted on the temperature-regulating block. At least one of the driving element and the nonlinear circuit structural element is contacted by the temperature-regulating block and the temperature of the contacted element is adjusted.
Next, operation of the above-described semiconductor laser device will be described.
The temperature of at least one of the driving element and the nonlinear circuit structural element can be adjusted because one of the driving element and the nonlinear circuit structural element (e.g. a self-multiplication circuit or a log amplifier) both mounted on the driving circuit substrate is contacted by the temperature-regulating block. As a result, effects of at least one of the temperature characteristic of the driving element and the input-output characteristics of the nonlinear circuit structural element can be avoided, and the amount of light of the light beam emitted from the emitting device can be stabilized. Further, at least one of the driving element and the nonlinear circuit structural element contacts the temperature-regulating block. Thus, as compared with a case in which the driving element does not contact the temperature-regulating block and is connected by a harness, effects due to external disturbance of a harness can be avoided. Thus, the light amount of the light beam emitted from the emitting device can be stabilized.
A second aspect of the present invention is a method for controlling a light amount of a semiconductor laser beam, comprising the steps of (a) making a portion of an emitted light beam incident obliquely onto a light-amount detecting section, (b) directly detecting the portion of the emitted light beam at the light-amount detecting section, (c) adjusting a temperature of a light beam emitting section to a constant temperature, (d) adjusting a temperature of the light-amount detecting section to a constant temperature, and (e) adjusting a light amount of the light beam on the basis of a detected value of the light beam.
In accordance with the present invention, accurate AP control can be carried out by directly detecting output light illuminated onto a photosensitive material.